Purification of in-polymer GlcUA-5-epimerase will be continued, using 5-3H-labeled partially N-sulfated (GlcNAc - GlcUA)n as assay substrate and release of H3 as the assay reaction. Enzyme source will be mast cell mastocytoma soluble fraction. Heparin synthesized from specifically H3-labeled GlcUA precursors will be converted chemically to the component uronic acids and the latter will be degraded carbon by carbon to locate the H3. Shift of label will be used to help determine the mechanisms of the in-polymer 5-epimerization of GlcUA which occurs during heparin biosynthesis. The same methods will be employed to examine the D-mannuronic to L-guluronic acid interconversion which occurs in the synthesis of alginic acid-like polymers by Pseudomonas and Azotobacter species. BIBLIOGRAPHIC REFERENCES: Structure and Biosynthesis of Heparin-like Polysaccharides. (1977). U. Lindahl, M. Hook, G. Backstrom, I. Jacobsson, J. Roesenfeld, A. Malmstrom, L. Roden and D.S. Feingold. Federation Proc. 36, 19. Biosynthesis of Heparin, Purification of the C-5 Uronosyl Epimerase from Beef Liver. (1977). L. Roden, A. Malmstrom, G. Backstrom, P. Campbell, D.S. Feingold, I. Jacobsson and U. Lindahl. Federation Proc. 37, 748.